Telephone system



April 29 1924.

R. S. WILBUR' TELEPHONE SYSTEM Filed Sept. 16,. 1920 4 Sheets$heet 1Aid/yum! //4 vex 1 for.-

April 29, 1924.

1,492,092 R. s. WILBUR TELEPHONE SYSTEM il p 16 1920 4 Sheets-Sheet 2April 29, 1924. 1,492,092

R. s. WILBUR TELEPHONE SYSTEM Filed Sept. 16 1920 Ray 5. mm

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April 29, 1924 1,492,092

R. s. WILBUR TELEPHONE SYSTEM Filed Sept. 16 1920 4 Sheets-Sheet 4 by WPatented Apr. 29, 1924.

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RAY S. WILIBUR, 0F LYNDHURST, NEW JERSEY, ASSIGNOB TO WESTERN ELECTRICCOMPANY, INCORPORATED, OF NEW YORK, N. Y., A GORPORATION OF NEW YORK.

TELEPHONE SYSTEM.

Application filed September 16, 1920. Serial No. 410,639.

To all whom it may concern:

Be it known that I, RAY SETH VVILnon, a citizen of the United States,residing at Lyndhurst, in the county of Bergen and State of New Jersey,have invented certain new and useful Improvements in Telephone Systems,of which the following is a. full, clear, concise, and exactdescription. 1

This invention relates to telephone systems and more particularly tosuch systems employing long transmission trunk lines over which bothtelephonic and signaling currents may be transmitted.

When long transmission lines interconnect widely separated oflices orexchanges, it has been the practice to introduce at either end aso-called inequality type repeating coil to inductively join the lineproper with the terminating apparatus at each station. These coils aredesigned to compensate for the difference at voice range frequenciesbetween the impedance of the internal or terminating section of the linecircuit and the apparatus associated therewith during conversation, ascompared with the impedance of the external section of the line circuit.By thus equalizing the impedances of these portions of the talkingcircuit, the voice currents are most efficiently transmitted from oneoiiice to the other.

In one system of this nature, it has been proposed to provide meansassociated with the inequality type coils, which will also eiiicientlytransmit therethrough signaling currents of infra voice frequencies,such as are ordinarily employed in signaling over the usual localsubscribers line circuits.

The object of this invention is to provide an improved signaling meansfor a system of this character.

One feature of the invention is the provision of means in a trunk linecircuit of this character, for controlling the incoming calling andsupervisory signals independently of the conversational circuits of theterminating sections of the line and of the associated operators linkcircuits.

A further feature of the invention resides in the provision of means forconverting the apparatus of the terminating sections of the line circuitfrom its normal condition, adapted to most efiiciently transmit voicecurrents to a condition adapted to most eliiciently transmit signalingcurrents when it is desired to signal the distant office.

These and other features of the invention not specifically mentionedabove, will be apparent from the following description and theembodiments thereof shown in the accompanying drawings, Figures 1 and 2of which show a telephone trunk line interconnecting two stations oroffices, in which the invention is embodied; Figures 3 and 4 showanother embodiment applied to a similar trunk line circuit; while Figure5 illustrates diagrammatically the Wheatstone bridge arrangement of aportion of the signal controlling apparatus shown in Figures 3 and 4.

Referring to the drawing, Figures 1 and 2 when placed end to end withFigure 1 at the left, show a long telephone trunk line circuit Cinterconnecting two telephone oflices or exchanges and X, andinductively coupled with internal or terminating sections B and Drespectively, by means of repeating coils 30 and 130. Windings 27, 28and 127, 128, respectively, cooperate during conversation with theassociated wind ings 23, 25 and 123, 125, respectively, such windingsbeing proportioned so as to provide the most efficient transmission ofvoice currents. Additional windings 22, 26, and 122, 126, associatedrespectively with windings 23, 25 and 123, 125 are so proportioned andassociated with the other windings so as to provide the most efiicienttransmission of the relatively low frequency signaling currents intocircuits containing responsive relays 20 and 120, respectively. Thesecircuits are tuned for the low frequency signaling current, while theypresent very high impedances to the higher or voice frequency currents.

The terminating sections B and D are provided with jacks 10 and 110respectively for cooperation with plugs 6 and 106 of operators cord orlink circuits A and E at offices W' and X respectively. Only suchportions of link circuits A and E are shown as are essential to a properunderstanding of the invention. Usual line lamps 16 and 116, busysignaling devices 14 and 114, and cord circuit supervisory lamps 5 and105 are provided at offices W and X respectively. These lamps anddevices are controlled by relays which) are associated with the sleeveconductors of the line and cord circuits, and are dependent upon theresponsive relays 20 and 120; Relays 19and 119 are also controlled byringing keys of the associated cord circuits A and E to provide a moreefficient path for the trans mission of the outgoing signaling currents.

Figures 3 and 4 when placed end to end with Figure 3'at the left show asimilar line circuit H, interconnecting offices Y and Z, and terminatingthereat in internal or terminating sections G and J for association withoperators cord or link circuits F and K. Usual line lamps 216 and 316,busy signal devices 214 and 314, and link circuit supervisory signallamps 205 and 305 are controlled by responsive relays 217 and 317,independently of the talking circuit conductors, as in the case of thesystem illustratedin Figures 1 and 2. However, the various operatingfeatures are obtained by varying the connections of relays andresistances at each office which are placed in the form of the wellknown Wheatstone bridge, having arms Q, R, S, T and a galvanometerconnection or portion U, as diagrammatically illustrated in Figure 5.The reference characters of the elements at each ofiice are shown inFigure 5 so that the same figure clearly shows the arrangement at bothofiices.

It is thought that the invention may be more fully comprehended from thefollowing description of the operation of the systems shown on thedrawings.

Referring to Figures 1 and 2 and assuming that the operator at office Wwishes to converse with the operator at office X, plug 6 of the cordcircuit A is inserted into the jack 10 of the terminating section B.Relay 11 is operated over a circuit extending from battery through thelamp 5, sleeve contacts of plug 6 and jack 10, andhigh resistancewinding 13 of relay 11 to ground. However, due to the high resistance ofwinding 13, lamp 5 does not receive sufficient current to cause itsillumination. The operation of Lelay 11 causes the operation of busysignaling device 14 over an obvious circuit and disconnects the linelamp 16.

The operator at office W. thereupon actuates the ringing key 4,establishing a circuit extending from the source oflow frequencysignaling current through the lower alternate contact of key 4,'the ringcontacts of plug 6 and jack 10, the lower normal contact of relay 19,the winding 26 of repeating coil 30, the winding of alternating currentrelay 20, the condenser 21, the winding 22 of repeating coil 30, theupper normal contact of relay 19, the tip contacts of jack 10 and plug6, and the upper alternate contact of key 4 to ground. The circuit pathincluding the winding of relay 20 and the condenser 21, being tuned tothe frequency of the signaling current being applied to the circuit justtraced, ordinarily of 16 cycles per second, relay 20 operates. A circuitis completed by the operation of relay 20, which extends from batterythrough the winding and the left-hand normal contact of relay 18, theright-hand alternate contact of relay 11, and the contact of relay 20 toground. Relay 18 thereupon looks over a circuit extending from batterythrough the winding and left-hand alternate contact'of relay 18, thecontact of relay 17, and the left-hand alternate contact of relay 11, toground. The closure of the middle alternate contact of relay 18 suppliesground to the low resistance winding 12 of relay 11, thereby shuntingthe high resistance Winding 1;; of such relay by the low resistancewinding 12, to increase the current flow through the lamp 5 suflicientlyto permit it to glow. The closure of the right-hand alternate contact ofrelay 18 causes the operation of relay 19 over an obvious circuit, sothat the ringing current thereafter traverses a circuit traced from thesource of signaling current, through the lower alternate contact of key4, the ring contacts of plug 6 and jack 10, the lower alternate contactof relay 19, the windings 26 and 25 of the repeating coil 30, thecondenser 24, the windings 23 and 22 of the repeating coil 30 in series,the upper alternate contact of relay 19, the tip contacts of jack 10 andplug 6, and the upper alternate contact of key 4 to ground.

Thus ringing current is efficiently induced into the secondary windings27 and 28 of the repeating coil 30 and traverses the external section ofthe trunk line circuit C to the oflice X, and flows through the windings127 and 128 of the repeating coil 130 thereat. By the medium of the coil130, these signaling currents are induced into the secondary windings122, 123, 125, and 126 thereof, and flow through the circuit tuned forsuch signaling currents, which includes the Winding of relay 120 and thecondenser 121. Relay 120 thereupon responds to such signaling currentand completes a circuit which may be traced from battery through thewinding and normal contact of relay 115, the left-hand normal contact ofrelay 111, and the contact of relay 120 to ground. Relay 115 thereuponoperates and is locked in an operated condition over a circuit traceablefrom battery through the winding and right-hand alternate contact ofrelay 115 and the middle normal contact of relay 111 to ground. The lamp116 is illuminated and busy signaling device 114 is operated overobvious circuits controlled by the closure of the left-hand alternatecontact of relay 115. After maintaining the ringing key 4 actuated forthe usual period, the operator at oflice W releases such key, whereuponrelay 20 releases, but relays 18 and 19 remain operated since they arecontrolled by the sleeve relay 11. In like manner, due to thediscontinnance'of the ringing current by the release of key at, relay120 roleases, but relay 115 remains 0 erated since it is controlled bythe sleeve re ay 111.

In response to the illumination of the lamp 116, the operator at officeX inserts plug 106 of cord circuit E into jack 110, thereupon completinga circuit from battery through lamp 105, the sleeve contacts of plug 106and jack 110 and the high resistance winding 112 of relay 111 to ground.Relay 111 operates due to the current flowing through such circuit, butdue to the high resistance of winding 112, such current is insufiicientto cause the illumination of lamp 105. The opening of the middle normalcontact of relay 111 causes relay 115 to release, thereby extinguishinglamp 116; but the closure of the middle alternate contact of relay 111before the opening of its right-hand normal contact maintains theoperations of busy signaling device 114 over an obvious circuit. Theclosure of the left-hand alternate contact of relay 111 shifts theconnection of the armature of relay 120 to the normal contact of relay118. while the closure of the righthand alternate contact of relay 111connects ground to the contact of relay 117.

The operator at ofiice 1V, upon releasing the ringing key t, actuatesthe listening key 2. thereby connecting the operators telephone set 1 tothe talking conductors of the link circuit A and the associatedterminating section B of the trunk line extending to the oflice X. Theclosure of the lower local contact of key 2 causes the operation of acommon marginal relay 3 over a circuit extending from battery throughthe winding of relay 3, the lower local contact of key 2. the sleevecontacts of plug 6 and jack 10, the low resistance winding 12 and thehigh resistance Winding 13 of the relay 11 in parallel and the middlealternate contact of relay 18 to ground. Relay 3 is made marginal andoperates only when, following the actuation of the listening key 2, thetwo windings 12 and 13 of relay 11 are in parallel relation as in thecase where the operator at otiice 1V had previously actuated the ringingkey 2 or an incoming ringing signal had been received prior thereto. Theoperation of relay 3 completes a circuit extending from battery throughthe contact of relay 3, the lower middle contact of key 2, the uppernormal contact of key 4, the tip contacts of plug 6 and jack 10, themiddle alternate contact of relay 19 and the winding of relay 17 toground. Relay 17 thereupon operates and opens the locking circuit ofrelay 18 which. in releasing, causes the release of relay 19 toreestablish the original talking condition of the terminating circuitthrough the normal contacts of such relay, as well as to open the branchcircuit including the low resistance winding 12 of relay 11, so that thehigh resistance winding 13 of relay 11 is placed directly in circuitwith the lamp 5 in multiple with the winding of relay 3. and the reducedcurrent flow extinguishes such lamp but does not cause the release ofrelay 3.

The operator at ollice X, after inserting the plug 106 into the jack110, actuates listening key 102 to connect the operators set with thetip and ring conductors of the link circuit E and the associatedterminating section I) of the trunk circuit, for conversationalpurposes. The closure of the lower local contact of listening key 102completes a circuit extending from battery through the winding of themarginal, common or positional relay 103, the lower local contact of key102, the sleeve contacts of plug 106 and jack 110, and the highresistance winding 112 of relay 111 to ground. However relay 103 ismarginal as in the case of relay 3 and does not operate when placed inseries with the high resistance winding 112 of relay 111, thereforebattery is not connected to the tip conductor of the cord circuit E andthe terminating section D of the trunk circuit. The operators maythereupon converse. the voice currents flowing through the windings 123,125, 127 and 128 of repeating coil 130 and the windings 27, 28, 23 and25 of the repeating coil 30, such windings being properly proportionedto etliciently transmit currents within the voice range of frequencies.

Upon the completion of the conversation the operators release thelistening keys 2 and 102, the release of key 2 causing the release ofrelay 3. The operator at office W thereafter actuates ringing key 4 tosend a disconnect signal to the oflice X. The actuation of such ringingkey completes a circuit similar to that originally traced upon the firstactuation of such key, and causes the operation of ringing responserelay 20 which again causes the operation and locking of relay 18 andthe consequent operation of relay 19. As in the previous case, theoperation of relay 19 changes the terminating section B of the trunkcircuit to a condition suitable for the transmission of the signalingcurrents through the proper windings of re peating coil 30 into theexternal section of trunk circuit C, extending to the ofiice X. Thesecurrents are received at the latter office through the proper windingsof repeating coil 130 and, as previously mentioned, cause the operationof relay 120 and thereafter the operation of relay 118 over a circuittrace able from battery through the winding and right-hand normalcontact of relay 118, the left-hand alternate contact of relay 111 andthe contact of relay 120 to ground. Relay 118 closes an obvious circuitfor relay 119,

which thereupon operates and interrupts the talking conductors of theterminating section D. The closure of the right-hand contact of relay118 com letes a locking circuit therefor, cxtending rom battery throughthe winding and right-hand alternate contact of relay 118, the contactof relay 117 and the right-hand alternate contact of relay 111 toground. The closure of the middle alternate contact of relay 118connects ground to the low resistance winding 113 of relay 111, therebyplacing such winding in parallel relation with the high resistanceWinding 112 of such relay permitting sufficient current to flow throughthe circuit including lamp 105 to cause its illumination to serve as adisconnect signal to the operator at olfice X.

The operator at office X may thereupon challenge by actuating thelistening key 102 connecting the operators set 101 to the conductors ofthe link circuitE, to ascertain Whether it is desired to discontinue theconversation. Due to the parallel relation of the high and lowresistance windings 112 and 113 of relay 111, relay103 receivessufiicient current to cause its operation. A circuit is therebycompleted from battery through the contact of relay 103, the middlelower contact of key 102, the upper normal contact of key 104, the tipcontacts of plug 106 and jack 110, the middle alternate contact of relay119 and the Winding of relay 117 to ground. In operating, relay 117interrupts the locking circuit for relay 118, which releases to causethe release of relay 119 to restore the conductors of the terminatingsection D to talkin condition. The ground is also removed rom the lowresistance Winding 113 of the relay 111 so that lamp 105 is extinguisheddue to the reduced current flow through its circuit including the highresistance winding 112 of relay 111. Upon finding that the operatorstelephone set at office W is disconnected, the operator at otfice Xremoves the plug 106 from the jack 110, thereupon restoring allapparatus to its normal condition.

Should the operator at oflice X fail to actuate listening key 102 tochallenge the disconnection, the apparatus at office X is restored tonormal upon the removal of the plug 106 from jack 110, since by this actrelay 111 will release, thereby opening the locking circuit of relay118, which releases and causes the release of relay 119.

Referring more particularly to Figures 3, 4 and 5 and assuming that theoperator at ofiice Y desires to converse with the operator 'at office Z,the plug 206 of the link circuit F is inserted into the jack 210 of theinternal section G of the trunk circuit extending to oflice Z. Byreferring to Flg.

5, it will be noted that various relay wind ings resistances andcontacts. of keys and relays are included in the well-known form of aWheatstone bridge, composed of the arms Q, R, Sand T, with thegalvanometer portion U including the windings of two of the relays. Theinsertion of the plug 206 into the jack 210 completes the arms Q and 'Sof the bridge including the galvanoineter portion U, but leavesuncompleted the arms R and T. Relays 208, 207, 232 and 234 operate. Theoperation of relay 207 prevents the illumination of supervisory lam 205,the circuit for which would otherwise be completed by the closure of theright-hand contact of relay 208. The closure of the left-hand contact ofrelay 208 includes the resistance 209 in the arm R of the bridge. Theoperation of relay 232 produces no material effect upon the system, atthis time, other than to extend a ground connection to the left-handalternate contact of relay 233. Relay 234 in operating, causes theoperation of a busy signaling device 214 over a circuit extending frombattery through the left-hand alternate contact of relay 234 and theWinding of electromagnetic signaling device 214 to ground. The openingof the middle normal contact of ,relay 234 opens the locking circuitnormally prepared for relay 235, and the opening of the righthand normalcontact of relay 234 followed by the closure of the right-hand alternatecontact thereof transfers the connection leading to the contact of relay217 from relay 235 to relay 231.

The operator at office Y thereupon actuates the ringing key 204, tocomplete a circuit for ringing or other signaling current extending fromthe source of such current through the lower alternate contact of key204, the ring contacts of plug 206 and jack; 210, the lower normalcontact of relay 219, the Winding 226 of the repeating coil 230, thewinding of ringing response relay 217, the winding 22-2 of the repeatingcoil 230, the upper normal contact of relay 219, the tip contacts ofjack 210 and plug 206, and the upper alternate contact of key 204 toground. The opening of the local contact of key 204 prevents theillumination of the supervisory lamp 205 during the ringing period.Relay 217 operates and causes the operation of relay 231 over a circuitextending from battery through resistance 237, the winding and normalcontact of relay 231, the right-hand alternate vcontact of relay 234,and the contact of relay 217 to ground. Relay 231 operating over thiscircuit, closes its left-hand alternate contact to complete the arm T ofthe Wheatstone bridge by including resistance 236 therein. Due to thebalancing of the bridge relays 207 and 232 release. Lamp 205 is notilluminated due to the local contact of key 204 being open. The closureof the middle alternate contact of relay 231 causes the operation ofrelay 219 over an obvious circuit and the operation of relay 233 over acircuit including the normal contact of relay 232. Relay locks undercontrol of relay 231. The closure of the right-hand alternate. contactofrelay 231, causes a locking circuit to be completed therefor,extending from battery through the resistance 237, and the winding andright-hand alternate contact of relay 231 to ground. The operation ofrelay 219 changes the path for the ringing current and such signalingcurrent is thereupon passed over a circuit extending from the source ofsignaling current through the lower alternate contact of key 204, thering contacts of plug 200 and jack 210. the lower alternate contact ofrelay 219, the windings 226, 225, 223 and 222 of repeating coil 230 inseries, with the condenser 224, interposed between windings 225 and 223,the condenser 221, the upper alternate contact of relay 219. the tipcontacts of jack 210 and plug 206 and the upper alternate contact of key204 to ground.

This current is induced into the external section H of the trunk circuitextending to the ofiice Z by-means of the cooperating windings 227 and228 of the repeating coil 230. The current, upon arriving at office Z,flows through the windings 327 and 328 of the repeating coil 330, and isinduced into the circuit including the ringing response relay 317 bymeans of the serially interconnected windings 322. 323, 325 and 326 ofrepeating coil The circuit including the winding of relay 317 and thelatter- Inentioned windings of repeating coil 330, is resonant to thefrequency of the signaling current impressed upon the line circuit bythe ringing key 204. Therefore, relay 317 operates and causestheoperation of relay 335 over a circuit extending from battery throughthe winding and normal contact of relay the left-hand normal contact ofrelay 334 and the contact of relay 317 to ground. Relay in closing itslct't-hand alternate contact. completes a locking circuit therefor,extending from battery through the winding and left-hand alternatecontact of relay 335 and. the middle normal contact of relay 334 toground. The closure of the right-hand alternate contact of relay 335completes obvious ,circuits for busy signaling device 314 and line lamp316.

The operator at oliice Z. observing the illumination of lamp 316,inserts plug 306 of link circuit K into the jack 310 of the terminatingsection J of the trunk line cir cuit extending to'the otlice Y. As inthe case of the equipment at office Y. certain of the apparatus atoitice Z cooperates to form a lVheatstone bridge, as-shown in Fig. 5.Following the insertion of the plug 306, the arms Q and S of the bridgeincluding the galvanometer portion U are completed, while the arms R andT are uncompleted.

Relays 308, 307, 332 and 334 which are serially included in thecompleted portions of the bridge operate in response to the currentflowing therethrough. The 0 eration of relay 307 prevents theillumination of the supervisory lamp 305, the circuit for which wouldotherwise be completed by-the operation of relay 308. The closure of therighthand contact of relay 308 includes the resistance 309 in the arm Rof the-bridge, but produces no other material effect at this time. Theoperation of relay 332 produces no material effect "at this time, exceptto extend a ground connection to the right-hand alternate contact ofrelay 333, the purpose of which will be evident from the furtherdescription of the operation. The operation of relay 334 causes theextinguishment of the lamp 316 by the opening of the righthand normalcontact of such relay, and by the closure of its right-hand alternatecontact relay 334 provides a substitute circuit to maintain the busysignaling device 314 in an operated condition, after the relay 335 isreleased by the opening of the middle normal contact of relay 334. Bythe opening of the left-hand normal contact and the closure. of theleft-hand alternate cont-act,

the conductor leading to the contact of relay 317 is transferred fromits normal connection with the winding of relay 335, to a connectionwith the winding of relay 331.

Assuming that the operator at office Y has restored the ringing key 204prior to the insertion of the plug 300 into the jack 310, the operatorat office Y actuates the. listening key 202, thereby opening the arm Rof the l-Vheatstone bridge at such otiice, and, as a result of thiscine-nit change. relays 207 and 232 again operate, relay 207, as before.preventing the illumination of lamp 205; but the operation of relay 232at this time completes a short circuit around the winding of relay 231.such circuit. including the left-hand alternate contact of relay 233 andthe alternate contact of relay 232. Relay 231 thereupon releases theopening of its middle alternate contact causing the release of relay219, which restores the terminating section Y of the trunk circuit toits normal talking condition, in which the conductors leading from thetip and ring contacts of the jack 210 are bridged by the windings 223and 225 of the repeating coil 230 interconnected by condenser 224. Theopening of the left-hand alternate contact of relay 231 also opens thearni'iv T of the bridge, but produces no other materialetfect at thepresent time. Relay 233 also releases, due to the opening of the middlealternate contact of relay 231, but no other effect is produced thereby.except to remove the short circuit established around the winding ofrelay 231.

After inserting the plug 306 into the jack l 310, the operator at ofiioeZ actuates listen ing key 302, thereby opening the arm R of the bridgeat such ofl ice. Such action, how

ever, produces no other material effect upon the system.- The closure ofthe alternate contacts of key 302, laces the operators telephone set 301in direct connection with the ti and ring conductors of the cord circuitI and the terminating section 5 of the trunk circuit. The operators atoffice Y and Z may thereupon converse over a circuit which is designedfor the most eiiicient transmission of currents of talking frequencies,such circuit including the normal contacts of the relays 319 and 219 andthe windings 323, 325, 327 and 328 of the repeating coll 330 at officeZ, and the corresponding windings 227, 228, 223 and 225 of repeatingcoil 230 at ofiice Y. The branch circuit including the ringing responserelay 217 and the windings 222 and 226 of repeating coil 230, and thecorresponding branch circuit including the ringing response relay 317and the windings 322 and 326 of the repeating coil 330 at oiiice Z,being adapted to receive the low frequency slgnaling current to the bestadvantage, and to present a very high impedance tothe higher frequenciesused in the transmission of the voice currents, do not materiallyinterfere with the conversation.

At the termination of the cpnversation, or whenever the operator atoifice Z wishes to signal the operator at otiice Y the actuation of theringing key 30 transmits current from the source of signaling currentthrough the lower alternate contact of the ringing key 304, the ringcontacts of plug 306 and jack 310, the lower normal contact of relay319, the winding 326 of repeating coil 330, the winding of relay 317,the winding 322 of repeating coil 330, the upper normal contact of relay319, the tip contacts of jack 310 and plug 306 and the upper alternatecontact of ringing key 304 to ground. Ringing response relay 317operates, causing the operation of relay 331 over a circuit extend ingfrom battery through the resistance 337, the winding and normalcontactof relay 331, the left-hand alternate contact of relay 33 1, andthe contact of relay 317 to ground. Relay 331 thereupon locks over acircuit extending from battery through the resistance 337 and thewinding and lefthand alternate contact of relay 331 to ground. Theclosure of the right-hand alternate contact of relay 331 completes thearm T including resistance 336, of the Wheatstone bridge at oiiice Z,and since the arm R has also been connected in circuit the bridge isthereby completed. The bridge is so designed that a balance now existsand relays 332 and 307 release since no current flows through portion Uof the bridge.

However, the lamp 305 is not lighted during While relay 319 is operated,the ringing current applied to the conductors of the cord circuit flowsthrough the alternate contacts of relay 319 and the windings 326, 325,323 and 322 of the repeating coil 330, the condenser 324, interposedbetween the wind ings 325 and 323, and the condenser 321.

These windings, when-cooperating with the windings 327 and 328' of therepeating coil 330, are particularly adapted for the transmission ofsignaling current of the character being applied to the cord circuit,and such signaling current is projected over the external section H ofthe trunk circuit to the ofiice Y, where it is induced through thewindings 227 and 228 into the windings 222, 223, 225, and 226 of therepeating coil 230, the windings 223 and 225 being separated by thecondenser 224, and then flows through the winding of ringing responserelay 217, causing its operation. The operation of relay 217 causes theoperation of relay 231 over a circuit extending from battery through theresistance 237, the winding and normal contact of relay 231, theright-hand alternate contact of relay 234 and the contact of relay 217to ground. The closure of the middle alternate contact of relay 231causes the op eration of relay 219, While the closure of the left-handalternate contact of relay 231 com pletes the arm T of the W'heatstonebridgr at ofiice Y by including the resistance 23 therein. The bridgecircuit is now com pleted and is so designed that it is now balanced,accordingly relays 207 and 232 receive no current and consequently re--lease. Relay 207, in releasing, completes a circuit extending frombattery through the local contact of key 204:, the contact of rela 207and the right-hand alternate contact of relay 208 and the lamp 205 toground. The illumination of the lamp 205 serves as a signal to theoperate at ofiice Y. The release of relay 232 cause the operation ofrelay 233 over a circuit ex tending from battery through themiddlalternate contact of relay 231, the windin and normal contact ofrelay 233 and the nor mal contact of relay 232 to ground. Relay 231thereupon locks over a circuit extending from battery through resistance237, and the win 3; and right-hand alternate contact of relay 231 toground. Relay 233 also i looks over a circuit extending frombatterythrough the middle alternate contact of relay 231, and the winding andright-hand alternate contact of relay 233 to ground.

In response to the illumination of the lamp 205, the operator at officeY may challenge by the actuation of the listening key 202 andfindingthat the signal is intended to serve as a disconnect signal, plug 206 isremoved from jack 210. The opening of the local contact of the listeningkey 202 opens arm R of the bridge whereupon relays 207 and 232reoperate. Relay 232 in operating completes a short circuit around thewinding of relay 231, which includes the alternate contact of relay 232and the left-hand alternate contact of relay 233. Re lay 231 thereuponreleases, causing the subsequent release of relays 233 and 21.9. Relays232 and 23 1 also release when the plug 206 is removed from the jack210, thereby restoring the busy signaling device 214 to normal. Relay217 is restored to normal upon the restoration of ringing key 304:.After the plug 206 is removed, or while removing such plug, the operatorat office Y maintains the listening key 202, actuated, thereby openingthe locking circuit of relay 208, which would extend from batterythrough the winding of relay 208, the local contact of key 202, theleft-hand alternate contact of relay 208 and the resistance 209 toground. Thus the release of relay 208 is insured.

in a like manner, the operator at office Z, after restoring the ringingkey 304, removes the plug 306 from the jack 310, causing similaroperations of the similar relays as described in connection with thedisconnection of the plug 206 from the jack 210. Similarly the operatorat office Z also maintains the listening key 302 actuated during theremoval of the plug in order to prevent the locking of the relay 308.All apparatus at each ofiice is thereby restored to normal.

What is claimed is:

1. In a telephone system, in combination, a transmission line having anexternal and a terminating section, a repeating coil having primary andsecondary windings, said primary and said secondary windings efficientlytransmitting currents within the voice 'ange of frequencies, additionalwindings for the repeating coil for cooperation with said windings forefficiently transmitting low frequency currents, a source of lowfrequency current, and switching means associated with the terminatingsection respon sive to said low frequency current for converting saidcoil from a condition for transmitting one of said currents to acondition for transmitting the other of said currents.

2. In a telephone exchange system, two offices, a trunk circuitextending between the offices, a terminating section at each oflice,

a repeating coil at each office having primary and secondary windingsfor giving a certain ratio of transformation, additional windingsassociated with each of said coils for giving a different ratio oftransformation, and switching means at each terminating sectionresponsive to the transmission of signaling current over the trunkcircuit for changing the ratio of transformation.

3. In a telephone exchange system, two otlices, a trunk circuitinterconnecting the offices, a terminating section associated therewithat each office, normally continuous conductors included therein, asource of signaling current at one otlice, switching means forassociating the source with the terminating section thereat, meansresponsive thereto to interrupt the conductors of both terminatingsections, an; operators telephone set at the first-mentioned office,additional switching means for connecting the telephone set with theassociated terminating section, and means responsive thereto forrestoring the continuity of the conductors of the associated terminatingsection.

4. In a telephone exchange system, two ofiices, a trunk circuitinterconnecting the ofiices, a source of signaling current at oneoffice, switching means thereat for associating the source with thetrunk circuit, means at the other office responsive to the current fromthe source, a trunk signaling device controlled thereby, means formaintaining the trunk signaling device operated after the release of theswitching means, a link circuit including a signaling conductor, asignaling conductor for the trunk circuit at said other ofiice, asupervisor signaling device associated with the link circuit andcontrolled over the signaling conductor thereof, means responsive to theconnection of the link circuit with the trunk circuit to remove thetrunk signaling device from and to transfer the supervisory signalingdevice to the control of the responsive means, a double wound relayincluded in the signaling conductor of the trunk circuit, and meansassociated with the trunk circuit to shunt one of the windings of therelay upon the actuation of the switching means during theinterconnection of the link and trunk circuits thereby operating thesupervisory signaling device and maintaining the supervisory signalingdevice operated after the release of the switching means.

5. In a telephone exchange system, two offices, a trunk circuitinterconnecting the offices, a source of signaling current at oneoffice. switching means thereat for associating the source with thetrunk circuit, means at the other office responsive to current from thesource, a trunk signaling device controlled thereby, means formaintaining the trunk signaling device operated after the release of theswitching means, talking and interconnected talking signalingterminating conductors for the trunk circuit at the other ofiice, a linkcircuit thereat including talking and signaling conductors forconnection with the trunk circuit, a supervisory signaling deviceassociated with the link circuit, means responsive to the connection ofthe link circuit with the trunk circuit to remove the trunk signal ingdevice from and to transfer the supervisory signaling device to thecontrol of the responsive means, means associated with the trunk circuitto operate the supervisory signalin device upon the actuation of theswitching means during the interconnection of the link and the trunkcircuits and to maintain the supervisory signaling device operated afterthe release of the switching means, said means including the signalingconductors of the trunk and link circuits, means associated with thelink circuit to connect a source of current to one of the conductors,and means controlled thereby to restore the supervisory signalingdevice.

6. In a telephone exchange system, two ofiices, a trunk circuitinterconnecting the offices, a source of signaling current at oneofiice, switching means thereat for associating the source with thetrunk circuit, means at the other ofiice responsive to the current fromthe source', a trunk signaling device controlled thereby, means formaintaining the signaling device operated after the release of theswitching means, a link circuit at the other oiiice for connection withthe trunk circuit, a supervisory signaling device associated therewith,means responsive to the connection of the link circuit with the trunkcircuit to remove the trunk signaling device from and to transfer thesupervisory signaling device to the control of the responsive means,means associated with the trunk circuit to operate the supervisorysignaling device upon the actuation of the switchin means duringinterconnection of the link an trunk circuits and to maintain the deviceoperated after the release of the switching means, an operatorstelephone set at the other oflice, switching means for associating theset with the linkcircuit, and means controlled over the interconnectedtalking conductors of the link and trunk circuits and responsive to theassociation of the operators set with the link circuit to release thesupervisory signaling device.

7. In a telephone exchange system, two offices, a trunk circuitinterconnecting the ofiices, a source ofsignaling current at one officeswitching means thereat to associate the source with the trunk, meansassociated with the trunk responsive to the signaling current, aterminal for the trunk circuit thereat including talking and signalingconductors, a link circuit including talkin and signaling conductorsconnected therewith, a

- 1,4eaoee supervisory signaling device associated with the linkcircuit, means controlled by the responsive means and includinginterconnected signaling conductors of the link and trunk to operate thesupervisory signaling device, and means associated with the trunkcircuit and controlled over one otthe interconnected talking conductorsof the link and trunk to restore the signaling device to normal.

8. In a telephone exchange system, a trunk circuit interconnecting afirst and a second ofiice, terminating sections therefor at each oiiiceincluding talking and signaling conductors, a'source of ringing currentat the first oiiice, means for connectingthe source to the associatedterminating section, a link circuit connected with the trunk circuit atthe second ofiice including talking and signaling conductors, .asupervisory signaling device thereat, a relay at the second ofiiceresponsive to the ringing current received from the first ofice tooperate the supervisory signaling device by means of current flowingover the interconnected signaling conductors of the link and trunkcircuits and to connect a second relay to one talking conductor of thetrunk circuit, and operator-controlled means included in the linkcircuit to operate the second relay by current flowing over one of theinterconnected talking conductors, thereby restoring thesupervisorysignaling device.

9. In a telephone system, line sections of different impedances for thetransmission of currents of difierent ranges of frequencies, meansinductively coupling said sections, said means compensating fordifferences in the impedances of the sections for the said ranges offrequencies, means operative incident to the establishment of aconnection over said sections for altering the inductive coupling ofsaid sections, a link circuit for connection with one of the linesections, a supervisory signal therein, and means associated withanother of the line sections for controlling said signal by the currentof one of the ranges over said line sections.

10. In a telephone exchange system, two ofiices, a trunk line extendingbetween said offices divided into inductively coupled sections for thetransmission of currents of different frequencies, said sections havindifl'erent impedances, means associated wit said sections operativeincident to the establishment of a connection over said sections forcompensating for the differences in impedances of the sections byaltering the inductive coupling thereof, a link circuit at one of theoffices connected to the trunk line, a supervisory signal therein, andmeans at the other ofiice for controlling said signal by one of saidfrequencies over said trunkline.

till

11. In a signaling system, a transmission line divided into sections,means for applying currents of various frequencies to said line, arepeating coil joining said sections,

5 and means selectively responsive to currents of different frequenciesapplied to said line to vary the ratio of transformation of saidrepeating coil.

12. In a signaling system, a signal trans- 10 mission path divided intosections, means for applying currents of various frequencies to saidpath, inductive repeating means joining said sections, and meansselectively responsive to currents of difi'erentfrequencics applied tosaid path to Vary the ratio of transformation of said inductiverepeating means.

I11 witness whereof, I hereunto subscribe my name this 11th day ofSeptember, A. D., 1920.

RAY S. WILBUR.

